Nondirectional speakers which spreadly emit out a voice in a direction in which an emitter is oriented have been widely used. On the other hand, there have been provided ultra-directional speakers which provide high directivity using the principle of parametric speakers. An ultra-directional speaker generates a sound having frequencies within the range of human hearing by using distortion components which are generated when a strong ultrasonic wave propagates through the air, and concentrates the generated sound to a front side thereof and makes it propagate, thereby offering sounds having high directivity. Such a parametric speaker is disclosed by, for example, patent reference 1.
A robot equipped with audiovisual system is disclosed by, for example, patent reference 2. This moving object equipped with audiovisual system can carry out a real-time process of performing visual and sound tracking on a target. This system also has a technology for unifying several pieces of sensor information about a visual sensor, an audio sensor, a motor sensor, etc., and, even if any one of the plural pieces of sensor information is lost, continuing the tracking by complementing the lost piece of sensor information.
Patent reference 1: JP,2001-346288,A
Patent reference 2: JP,2002-264058,A
Since a speaker which is mounted in a related art moving object is a low-directional speaker, a voice generated by the related art speaker reaches an indefinite number of things which exist around the moving object. For this reason, a related art speaker cannot provide voice information for a specific limited region.
In general, a related art ultra-directional speaker emits a voice in directions which are limited only to a region having an angle of 20 degrees in a direction of the front of an emitter, and does not have a function of automatically changing the direction of the front of the emitter to a direction in which the voice is to be emitted.
Conventionally, the adjustment of the level of the voice generated by the emitter of the related art ultra-directional speaker is manually performed, and the related art ultra-directional speaker does not have any function of adjusting the voice level according to a position to which the related art ultra-directional speaker provides the sound.
In addition, a problem with a case where a low-directional speaker is applied to a talking device of a robot communications system is that it is difficult for the robot communications system to recognize a voice from another sound source while the talking device is making a voice. To be more specific, a robot's microphone is disposed closer to the robot's drive motor compared with other sound sources, such as a partner to which the robot is talking. As a result, even if the absolute power of noise caused by the drive motor is small compared with those of other sound sources, the power of the motor noise collected by the microphone becomes relatively large and has an influence on voice recognition.
In addition, since the low-directional speaker emits a voice so that the voice can reach a partner to which the robot is going to talk, the output power of the voice is set to be large than that of the motor noise. Since such a voice outputted by the robot becomes noise at the time of recognizing a voice from the partner, the signal-to-noise (S/N) ratio becomes small as a result and it is therefore difficult for the robot to perform voice recognition. For this reason, a related art robot with a low-directional speaker turns off a hearing function while it is talking with a partner, or recognizes a voice from the partner by receiving it via not-the robot's microphone, but the microphone of a head set or the like, which is placed in the vicinity of the partner's month.
The present invention is made in order to solve the above-mentioned problems, and it is therefore an object of the present invention to provide an ultra-directional sound system that can surely provide a voice to a moving target to which the voice is to be provided, and which can provide voice information having an optimal volume in a direction of the target to which the voice is to be provided.
It is another object of the present invention to provide a moving object equipped with ultra-directional speaker which constitutes a robot communications system which implements a simultaneous dialog function and a high-concealment whispering function.